Previously, as this kind of electromagnetic clutch mechanism, a so-called flat-spring-hub-type electromagnetic clutch mechanism, which uses flat springs to enable and disable transmission of a rotational drive force from a pulley (serving as a driving-side rotatable body) to an armature (serving as a driven-side rotatable body), is disclosed in, for example, the patent literature 1.
In the flat-spring-hub-type electromagnetic clutch mechanism, when an electromagnet is energized, the armature is attracted to the pulley and is coupled to the pulley to transmit the rotational drive force from the pulley to the armature. In contrast, when the electromagnet is deenergized, the armature is displaced away from the pulley by a resilient force, i.e., a reaction force of the respective flat springs, and thereby the transmission of the rotational drive force is disabled.
More specifically, the armature and an inner hub are coupled with each other through the flat springs, and the armature is displaced by the resilient force, i.e., the reaction force of the respective flat springs in a direction away from the pulley.
Lately, because of an increased need for reducing NV, i.e., an increased need for reducing the noise and vibration and an increased need for the low costs, it is very promising to reduce the operational sound of the flat-spring-hub-type electromagnetic clutch mechanism that has the simple structure.
For example, in the prior art technique disclosed in the patent literature 1, a rubber member is placed between the armature and each flat spring such that the operational sound is reduced by alleviating the vibrations of the armature generated at the time of colliding the armature against the pulley upon attracting of the armature toward the pulley. Specifically, the rubber member is placed between a surface of the armature, which is shaped in a form of a generally planar surface, and a surface of the flat spring, which is shaped in a form of a generally planar surface.
Furthermore, previously, a so-called rubber-hub-type electromagnetic clutch mechanism is disclosed in, for example, the patent literature 2. The rubber-hub-type electromagnetic clutch mechanism implements the reaction force, which separates the armature from the pulley, through use of a rubber member instead of the flat springs.
According to the prior art technique disclosed in the patent literature 2, a hub plate is joined to the armature, and the hub plate and the inner hub are connected together through the rubber member, which is shaped into a ring form. The armature and the hub plate are displaced away from the pulley by an elastic force, i.e., a reaction force of the rubber member.
Furthermore, the patent literature 2 recites that a projection, which is molded integrally with a radially outer part of the rubber member, is clamped between the hub plate and the armature to reduce the operational sound.